Hydraulic lash adjuster for an internal combustion engine

ABSTRACT

A hydraulic lash adjuster for a valve train of an internal combustion engine is provided, with the hydraulic lash adjuster including a circular cylindrical housing in which a piston ( 22 ) is arranged for axial displacement, and further including a one-way valve ( 31 ) with a closing body ( 32 ) that can be brought to bear against a valve seat ( 28 ) of the piston ( 22 ) for sealing a through-opening ( 24 ). The closing body is surrounded by a valve cap ( 35 ) and loaded by a compression spring ( 33  that is supported with a first end on the closing body ( 32 ) and with a second end on the valve cap ( 35 ). The closing body ( 32 ) has an approximately spherical, convexly vaulted bearing surface ( 34 ) for sealing contact on the valve seat ( 28 ) and deviates in shape from a ball shape.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application60/802,929, filed May 24, 2006, which is incorporated by referenceherein as if fully set forth.

FIELD OF THE INVENTION

The invention relates to a hydraulic lash adjuster for the valve trainof an internal combustion engine, said hydraulic lash adjustercomprising a circular cylindrical housing, in which a piston is arrangedfor axial displacement, and further comprising a one-way valvecomprising a closing body that can be brought to bear against a valveseat of said piston for sealing a through-opening, said closing bodybeing surrounded by a valve cap and loaded by a compression spring thatis supported with a first end on the closing body and with a second endon the valve cap.

BACKGROUND OF THE INVENTION

For a plurality of technical reasons, it is desirable to reduce the sizeof a hydraulic lash adjuster (HLA) used in the components of a valvetrain. This would be apparent, for example, for the development of aswitchable tappet for a tappet push rod motor. One of the factorsdetermining the minimum height of an adjuster is the height of theone-way valve, which typically contains a ball as a closing body. Ifthis height can be reduced, then the entire height of the adjuster canalso be reduced.

In the publication DE 40 23 885 A1, which concerns a roller tappet withhydraulic lash adjustment, the disadvantage is mentioned that rollertappets known up until then were constructed with relative large volumesand had an increased overall height especially compared withconventional cup tappets. Accordingly, measures should already have beendisclosed there, with whose help the dimensions of roller tappets withhydraulic lash adjustment could be reduced. For achieving this goal, inthis publication it is proposed, e.g., for the one-way valve device,through which a hydraulic high-pressure chamber connects to a hydraulicstorage chamber, to use several one-way valves, which are then arrangedone next to the other. In this way, the associated storage chamber witha typical, relatively large volume can be divided into severalsub-chambers, which can then be arranged in a construction, which hasbeen optimized in the sense of installation space, at suitable freespaces in the roller tappet.

A hydraulic lash adjuster of the type noted above is known from thepublication DE 198 44 202 A1. This adjuster constructed as a rollertappet features the mentioned disadvantage of the large-volumeconstruction with increased overall height relative to conventional cuptappets.

SUMMARY OF THE INVENTION

The invention is based on the objective of reducing the installationsize of a hydraulic lash adjuster to be used in a valve train of aninternal combustion engine.

This objective is met according to the invention in that the closingbody features an approximately spherical, convexly vaulted bearingsurface for the sealing contact on the valve seat and, incidentally,deviates in shape from a ball shape. In this way, in the minimuminstallation height of the adjuster, the entire diameter of a ball isnot included, as was used in previously known elements as a closingbody. Instead, in contrast to these previously known elements, thesupport point of the compression spring can be located significantlycloser to the valve seat in the arrangement according to the invention.Consequently, the length dimension of the installation space, which isdetermined by the closing body and the compression spring, can besmaller.

The closing body can have, for example, a mushroom shape. In this case,the compression spring, when it is constructed as a cylindrical, helicalcompression spring, can partially surround the shaft of the closing bodymushroom concentrically and can be supported on the bottom side of themushroom head of the closing body in the vicinity of the valve seat.

It is also possible for the closing body to have a dome shape. Then thecompression spring can project partially into the hollow space of theclosing body dome and can be supported there on the closing body in thearea of the vaulting in the vicinity of the valve seat.

The invention thus offers two solutions leading to the reduction of theheight of the one-way valve unit and thus also to the reduction of theheight of the overall lash adjuster. Here, one of the factorsdetermining the minimum size of the element is the size and shape of theclosing body of the one-way valve.

BRIEF DESCRIPTION OF THE DRAWINGS

Two embodiments of the invention are shown in the drawing and aredescribed in more detail below in comparison with a previously knownvalve train. Shown in each of the Figures in a longitudinal section are:

FIG. 1 is a longitudinal cross-sectional view of a lash adjusteraccording to the invention in a first construction;

FIG. 2 is a longitudinal cross-sectional view of a lash adjusteraccording to the invention in a second construction;

FIG. 3 is a longitudinal cross-sectional view of a valve train installedin an internal combustion engine with a previously known lash adjuster;

FIG. 4 is a partial representation in a longitudinal cross-sectionalview of the previously known lash adjuster enlarged relative to FIG. 3;

FIG. 5 and FIG. 6 are longitudinal cross-sectional views of the one-wayvalve of the lash adjuster shown in FIG. 3 and FIG. 4, respectively, inan enlarged representation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The hydraulic lash adjuster 1 shown in FIGS. 3 and 4 according to thepreviously known state of the art is installed in a valve train 2 of aninternal combustion engine 3, which can be actuated via tappet push rods4. The adjuster 1 is constructed as a switchable cam follower and iscomprised of an outer cylindrical section 5, which encloses in itsinterior 6 an inner cylindrical section 7. The section 7 can moveaxially relative to the outer section 5 and forms with this outersection a circular cylindrical housing.

The outer section 5 is closed with one end facing a cam 8 of a camshaftand by a base 9. In the area of the base 9 there is a roller 10, whoseouter surface is used as a contact surface for the cam 8. The roller 10is supported on a pin via a roller bearing. This pin is led in the areaof the base 9 diametrically through the outer section 5 and fixed therewith its end in the outer section 5 by stamping. With its end locatedoutside of the outer section 5, the inner section 7 faces the tappetpush rod 4, which here is supported with its end 12 on a dome-shapedbearing surface 11 of the inner section 7.

Hydraulic medium can be led to an outer end of a switching element 13causing the switching process of the adjuster 1. For this purpose, achannel 14 is provided in the internal combustion engine 3. Forachieving a large stroke of a gas-exchange valve 15 of the internalcombustion engine 3, wherein said gas-exchange valve is connected to theadjuster 1 via a valve lifter 16 and the tappet push rod 4, the couplingof the outer section 5 to the inner section 7 of the element 1 isrequired. The switching element 13 is produced as a piston-like slide,which is held in the coupling position by a compression spring.

If it is desired to disconnect the gas-exchange valve 15, then hydraulicmedium is led out of the channel 14 in front of the outer end of theswitching element 13. If the adjuster 1 is located in its base-circlephase, in which the outer section 5 and the inner section 7 are notfixed relative to each other, then for sufficient pressure of thehydraulic means, the switching element 13 can be displaced radiallycompletely into the inner section 7 against the force of its compressionspring. In the subsequent cam stroke, the outer section 5 is thendisplaced relative to the inner section 7 against the force of acompression spring 17 arranged in the outer section 5. In this case, thetappet push rod 4 and the gas-exchange valve 15 are not displaced,because the force of the compression spring 17 of the outer section 5 issmaller than the counteracting force of a compression spring 20 of thegas-exchange valve 15.

As a hydraulic lash adjuster, the adjuster 1 requires the supply of oilas the hydraulic medium. For this purpose, a feed line 18 is arranged inthe tappet push rod 4. Instead of this feed line, however, a feed linefor hydraulic medium is also conceivable, which leads in the internalcombustion engine 3 into the receptacle space 19 for the outercylindrical section 5.

The inner cylindrical section 7 of the lash adjuster 1 is a rotationallysymmetric housing part. It has a pocket hole, which forms ahigh-pressure chamber 21. A hollow cylindrical piston 22 is guided withseal lash in the housing part. This has a lower piston head and an upperpiston head. Underneath the lower piston head is the high-pressurechamber 21. Above the lower piston head is a low-pressure chamber 23,which is formed by the interior of the piston 22 and which is used as anoil storage space.

The high-pressure chamber 21 is connected to the low-pressure chamber 23via a central through-opening 24 (FIGS. 5 and 6), which is arranged inthe lower piston head. It is part of a one-way valve 27 provided with aclosing body 25 and a compression spring 26. This extends into thehigh-pressure chamber 21 underneath the lower piston head, wherein thethrough-opening 24 ends at a valve seat 28 of the piston 22 for asealing contact on the closing body 25 in the closed state of theone-way valve 27. Another compression spring 29 is supported in thehigh-pressure chamber 21 at its base. It applies force to the piston 22via a valve cap 30 surrounding the closing body 25 with its compressionspring 26.

The lash adjusters according to the invention shown in FIGS. 1 and 2differ from this previously known element by the modified constructionof each one-way valve.

In FIG. 1, the one-way valve 31 has a mushroom-shaped closing body 32.This contacts the valve seat 28 of the piston 22 due to the effect ofits compression spring 33 with an approximately spherical, convexlyvaulted bearing surface 34 and therefore closes the through-opening 24of the piston. The compression spring 33, which is arranged with themushroom-shaped closing body 32 in a corresponding valve cap 35contacting the piston 22 and which is supported on this cap with oneend, surrounds the shaft of the closing body 32 coaxially over part ofits length. It has a cylindrical, helical compression springconstruction and is supported with its other end on the bottom side ofthe mushroom head of the closing body 32. In this way, the overallheight h₂ of the one-way valve 31 in FIG. 1 is less than the overallheight h₁ of the previously known one-way valve 27 in FIG. 5 by thedifference h₃.

In FIG. 2, the one-way valve 36 has a dome-shaped closing body 37, whichcontacts the valve seat 28 of the piston 22 due to the effect of itscompression spring 38 with a similarly approximately spherical, convexlyvaulted bearing surface 39 and therefore closes the through-opening 24of the piston. The compression spring 38 is arranged together with thedome-shaped closing body 37 in a corresponding valve cap 40 contactingthe piston 22. It is supported on this cap with one end and projectswith a part of its length into the dome-shaped closing body 37, withwhich it is arranged coaxially. With its other end, the compressionspring 38 is supported on the inside of the closing body 37 in the areaof its vaulted bearing surface 39. In this way, the overall height h₄ ofthe one-way valve 36 in FIG. 2 is less than the overall height h₁ of thepreviously known one-way valve 27 in FIG. 6 by the difference h₅.

The present solution was designed as one possible construction for theinstallation of a switchable tappet for a tappet push-rod motor, but canalso be applied in the development of other lash adjusters.

LIST OF REFERENCE SYMBOLS

-   1 Lash adjuster-   2 Valve train-   3 Internal combustion engine-   4 Tappet push rod-   5 Outer cylindrical section-   6 Interior-   7 Inner cylindrical section-   8 Cam-   9 Base-   10 Roller-   11 Bearing surface-   12 End of tappet push rod-   13 Switching element-   14 Channel-   15 Gas-exchange valve-   16 Valve lifter-   17 Compression spring-   18 Feed line-   19 Receptacle space-   20 Compression spring-   21 High-pressure chamber-   22 Piston-   23 Low-pressure chamber-   24 Through-opening-   25 Closing body-   26 Compression spring-   27 One-way valve-   28 Valve seat-   29 Additional compression spring-   30 Valve cap-   31 One-way valve-   32 Closing body-   33 Compression spring-   34 Bearing surface-   35 Valve cap-   36 One-way valve-   37 Closing body-   38 Compression spring-   39 Bearing surface-   40 Valve cap-   h₁ Overall height-   h₂ Overall height-   h₃ Difference-   h₄ Overall height-   h₅ Difference

1. Hydraulic lash adjuster for a valve train of an internal combustionengine, said hydraulic lash adjuster comprising a circular cylindricalhousing in which a piston is arranged for axial displacement, andfurther comprising a one-way valve comprising a closing body that can bebrought to bear against a valve seat of said piston for sealing athrough-opening, said closing body being surrounded by a valve cap andloaded by a compression spring that is supported with a first end on theclosing body and with a second end on the valve cap, and the closingbody has an approximately spherical, convexly vaulted bearing surfacefor a sealing contact on the valve seat and deviates in shape from aball shape.
 2. Adjuster according to claim 1, wherein the closing bodyhas a mushroom-shaped construction.
 3. Adjuster according to claim 1,wherein the closing body has a dome-shaped construction.
 4. Adjusteraccording to claim 1, wherein the compression spring applying a force onthe closing body is constructed as a helical compression spring.